As with many commercial processes, it is desirable to maximize quality and yield with minimal sacrifice to time and expense associated with production of polytrimethylene ether glycol or copolymers thereof.
Highly purified polytrimethylene ether glycol (hereinafter also referred to as “PO3G”) is visually colorless, which is a desired feature for many commercial end-use applications in polyurethanes and other thermoplastic elastomers. However, the synthesis of low-colored PO3G or copolymers thereof has generally required very long reaction times or extensive pre- or post-processing resulting in additional manufacturing costs. PO3G produced from the acid catalyzed polycondensation of 1,3-propanediol (hereinafter also referred to as “PDO”) is highly influenced by the quality of monomer and processing conditions, such as reaction temperature, reaction time, catalyst concentration and water concentration. Pre-polymerization treatment methods are disclosed in the prior art to remove color precursors present in the PDO (see, for example, U.S. Pat. No. 6,235,948). Attempts have also been made to reduce the color of polytrimethylene ether glycols post-polymerization. For example, Sunkara et al. disclose a process for reducing color in PO3G by contacting PO3G with an adsorbent and then separating the PO3G from the adsorbent (U.S. Pat. No. 7,294,746).
Pre- or post-polymerization methods may undesirably add additional steps, time and expense to production processes for PO3G. Attempts have also been made to alter reaction conditions to control PO3G color during polymerization. For example, U.S. Patent Application Publication No. 20050272911 discloses methods of controlling color formation by carrying out the dehydration-condensation reaction in the presence of a catalyst composed of an acid and a base. U.S. Patent Application Publication No. 20090118464 discloses methods of reducing color by maintaining the water concentration in the reaction mixture above at least about 0.08% by weight.
One way to improve yield for a polymer production process is to minimize reactant loss during polycondensation. U.S. Pat. No. 5,635,590 discloses methods of decontaminating ethylene glycol from ethylene glycol/water mixtures formed during the esterification of terephthalic acid with ethylene glycol. In this process, the contaminated ethylene glycol is subjected to preliminary distillation for separation from water and low-boiling fractions and further processing before it is resupplied to the polycondensation process as decontaminated ethylene glycol.
Thus, a need exists for improved and convenient methods to reduce color and minimize yield loss in the production of PO3G and copolymers thereof.